The use of vascular angiography systems, particularly in cardiovascular surgery, has long been known, particularly in connection with preoperative mapping of the cardiovascular system to be operated upon for the purpose of surgical grafting or the like, and also in connection with ascertaining, after grafting, the effectiveness of the grafting, both as regards the subsequent free flow of blood through the graft to the revascularized conduit and the absence of leakage, or kindred defects.
To this end, both ultrasonic and X-ray angiography have been employed but in both cases considerable disadvantages arise, such as for example the undesirable contact between the ultrasonic probe and the exposed blood vessels, the necessity to inject into the blood vessels a suitable toxic contrast medium, and the inherent risk associated with the use of X-ray radiation.
It is as a consequence of these and other disadvantages that there has been proposed to use a cardiovascular angiographic system which is based on the thermographic technique and which involves obtaining infra-red thermal images of the relevant cardiovascular region prior to, during and subsequent to surgery. The relevant information which can be derived from such infra-red imaging arises in view of the fact that a temperature difference is established between the fluid (either cardioplegia or blood) flowing in the relevant blood vessels and the surrounding region. Thus, for example, such temperature differences can arise as a result of the initiation of fluid flow through a graft or the perfusion of blood into the surrounding tissue.
Proposals for the use of such infra-red coronary angiography have appeared in the professional literature and in this connection attention is particularly directed to the paper by Friedrich W. Mohr et al in The Annals of Thoracic Surgery, 1989; 47:441-9, entitled "Thermal Coronary Angiography: A Method for Assessing Graft Patency and Coronary Anatomy in Coronary By-pass Surgery". A proposal for a system for carrying out such angiography and clearly derived from the Mohr paper is to be found in U.S. Pat. No. 4,995,398.
These proposals have not, however, led to a practical system and have all been characterized by serious limitations which, in use, renders it impossible or difficult to employ them for real time infra-red imaging.
It is therefore an object of the present invention to provide a new and improved infra-red vascular angiography system particularly for use in cardiovascular surgery, in which the above-referred-to disadvantages are substantially reduced or overcome.